An isolation layer may be formed to define an active region and a field region in a semiconductor device. For example, a trench may be formed at an upper portion of a semiconductor substrate, and an insulation layer filling the trench may be formed on the semiconductor substrate. A thermal treatment and a polishing process may be performed on the insulation layer to form the isolation layer.
However, various processes performed with respect to the insulation layer may cause chemical, mechanical and/or electrical defects in the resulting semiconductor substrate.